


Don't Tell Anyone

by daemonhart



Category: Undertale (Video Game)
Genre: Begging, Child Abuse, Daddy Kink, Emotional/Psychological Abuse, Father/Son Incest, Incest, M/M, Non-Consensual, Parent/Child Incest, Pre-Canon, Rape, Sexual Abuse, Tentacle Dick, Underage Rape/Non-con
Language: English
Status: Completed
Published: 2018-02-12
Updated: 2018-02-12
Packaged: 2019-03-17 07:09:10
Rating: Explicit
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 1,354
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13654011
Author URL: https://archiveofourown.org/users/daemonhart/pseuds/daemonhart
Summary: [Drabble] Before the accident in the CORE, before the creation of Papyrus, Gaster had a secret project he was working on -- a manufactured monster, Sans, born of his own bones. When one locks themselves in a laboratory basement for weeks on end, though, one grows callous in the pursuit of satiating certain urges.





	Don't Tell Anyone

**Author's Note:**

> I subscribe to the headcanon that Papyrus and Sans were both created by Gaster from his own magic, perhaps using the bones of his hands as a source. Sans served as a sort of "failed prototype" who never really got over how worthless his father made him feel. I imagine this incident was just one of many that he was subjected to.
> 
> Likewise, I imagine Sans took after his father in how he spoke, at least until he realised he'd never be good enough and just gave up on the formality. In this scene, he's still trying to meet his father's impossible expectations.

“Ah, that’s a good boy…” cooed Gaster in his soft but deep voice. “A bit higher. I need to examine you properly…” His hand gave a tap on the back of the small skeleton’s sacrum, and the young monster obeyed. He hated these exams. He wasn’t sure why, but they always left him feeling terrible and gross. The scientist’s thumb and forefinger rolled across the tiny yet sensitive bones of Sans’ coccyx, which prompted an almost instinctive response to raise even higher. “There you go. Now, show daddy your ‘secret parts’. I assume you’ve been good and not mentioned this to anyone?”

“no, father. it’s a special part of my training,” Sans said flatly in rehearsed response. He’d been told that this was a good way for Gaster to check on the strength of his developing magic. What reason had he to disbelieve? So once he summoned his little flaccid dick and small hole, he made no protest against as two of his father’s fingers plunged roughly inside. However, he did give a whimper of pain. His fingertips scraped the lab tiles. “father, it hurts…”

Gaster snorted. “Perhaps if you remembered to do as I say, I wouldn’t treat you so roughly. Go on, then. What have I told you about calling me ‘father’? It’s far too formal.” Regardless of the discomfort, he slowly worked the digits in and out of the conjured magic. Soon enough, the whines stopped and Sans grew quiet.

“r-right, daddy…” he mumbled. He felt another finger enter, but this time his body offered little resistance. It was beginning to remember this training and reacted automatically. “do i look healthy fa–i mean, daddy?” His father laughed under his breath.

“Ah, no. It seems like your magic is a little weak today. Daddy will need to share some of his, but it’s alright. I’m happy to spoil my little one~” A low, predatory chuckle rumbled in his skull. “Don’t tell anyone. I don’t want to share with anyone but you. Understand?”

Don’t tell anyone. That message had been drilled into the young skeleton’s mind practically since his creation. He needed to protect his father’s secret training methods, so he obeyed, even if he felt disgusting. Don’t tell anyone. Even though he told Gaster he didn’t like it, the scientist didn’t listen. It was for Sans’ own good, he’d said, so don’t tell anyone. The admonishment echoed in his head as he brought his ribs to the ground and his ass in the air. Gaster’s fingers thrust a few more times before sliding free and wiping the leftover ectoplasm across the back of his son’s femur. “You adapted quickly this time. I didn’t even need to stretch you,” Gaster praised. “Do you like it that much?”

 _No!_  he wanted to shout, but even if his father was being gentle now, he knew the kinds of punishments that awaited if he resisted. “yes, daddy…will you fill me, please?” he recited. Sans’ eyes winced shut the moment he heard his father’s pants coming undone. Dread gathered in his SOUL, but this was necessary. All fathers made their sons strong this way, or so he had been told. Besides, it’s not like it felt bad…so why did he detest it so much? The blue muscle twitched once it felt the tip of Gaster’s tapered, sluglike appendage rub against it, but was helpless to stop its advance. Sans whined the moment it wriggled past and his father’s hips rolled forward. “ahh! daddy~ it feels so big…”

Gaster glided his hands down the back of his construct’s ribs. “It’s nice and swollen for you, Sans. If you help, I’m sure there’s lots of magic for me to share,” he purred. His grip found purchase on each of the other male’s ilia in preparation for the act itself. The scientist ground forward again and savoured the desperate sound his son made. “Remember those words I taught you? They make daddy  _very_ excited…Go on. Give it a try.”

Sans licked his teeth nervously, but as that slick, tarry cock burrowed deeper, his thoughts felt hazy. Still, his training was practically etched into his bones. The command dragged the phrases to the surface. “d-daddy, fuck me~” he cried without fully understanding its meaning, “fuck me hard…i wanna be your little slut…” He earned a sharp thrust for his reward and felt his own dick starting to harden. Father told him that meant he liked what was happening. It felt true at the time, but why was he always so sad after?

He didn’t have time to think on it.

The scientist began his breeding in earnest, bracing against his son’s pelvis so each pound had that much more momentum. His bones smacked hard against Sans’ still-growing ones every time he hilted himself and left behind marks that would definitely become bruises later. It hurt. Gods, it hurt, but at the same time, it made that thing between his legs feel so good. One of Sans’ hands tucked beneath himself and took hold of the rigid flesh, then gasped. Gaster’s face twisted into a grin. “Touching yourself, little one? You really are a slut for daddy’s dick…It’s alright. I’ll come soon and give you just what you’re looking for…” It wasn’t so much what he said, but how he said it that made the smaller monster moan. That low, dominant voice growling at him sent shivers along his spine.

“yes…! more, daddy! it feels so good~” Sans begged. His hand closed around his little erection with greater confidence now that he knew it pleased his father. Quick, firm strokes worked his shaft and the sensation of his own foreskin dragging over the glans brought him tremors. White spots danced in his vision. The inexperienced monster was quickly approaching climax, but so was Gaster; his son’s hole was starting to clench and flex so much, the stimulation was overwhelming. “please…ah, please!” Sans cried out, “i want…i-i want…”

Gaster noticed him stumbling over his words. He craned his head down beside the other’s and smiled. “You want me to ‘come’ in you, Sans. You want all that magic to stretch you out,” he murmured.

Sans nodded emphatically and tried to lick some drool that escaped his mouth, but only managed to smear it before another moan yanked his attention away. “y-yeah! come in me~” he begged, “make me feel good, daddy…!” The sound of his young voice was more than enough to push his father over the edge. Inky semen shot in thick loads into Sans’ conjured space, forcing it to swell to contain it all. Orgasm struck the smaller monster as well, and he trembled violently beneath Gaster, but his throbbing cock did not shoot anything like his father’s did. The older monster kept Sans held on his dick until every last drop had been taken. Pulling free prompted a gasp from the child, who allowed himself to collapse.

Now that it was over, he was acutely aware of himself. The slimy feeling of his father’s fluids leaking from his over-stretched hole. The way his body betrayed him by enjoying itself even when his mind screamed no. The fact that there was nobody he could talk to about it…He was so alone. Tears gathered, then escaped from the bottoms of his sockets. Why was he crying? Wasn’t it what he wanted? It felt good, right? Gaster stood and readjusted his pants before securing them again. When he spoke, his voice had returned to its usual cold rigidity. “Very good. Perhaps next time, we’ll use your mouth. I am not sure if you are yet old enough, but I cannot continue to risk giving you a child.” A few tugs to straighten his coat. “Once you’ve gotten yourself together, return to your chambers. I’ll issue you further training tonight. You did well to satisfy  _daddy_ , but do not misunderstand. You will not receive special treatment for doing your job as my construct.” With that, his back turned and he left the medical bay to return to his office.

Don’t tell anyone.  _Don’t tell anyone_.


End file.
